As the size of networked systems increases from a few connected computers located near each other to several thousand machines of various types and sizes scattered at great distances from each other, the demands on the network printers also increase. One of the most challenging demands in the implementation of network printers is connectivity. Typically, the network printer is a stand-alone peripheral device which is desired to perform in an increasing number of network and non-network communication environments. In network environments, the printer is desired to provide "seamless plug and play" connectivity for the continuous expansion of network service protocol/ports. For example, known network service protocol/ports that are desired to communicate with network printers are: printer access protocol (PAP)/LocalTalk (LT); PAP/EtherTalk (ET); transmission control protocol/internet protocol (TCP/IP); TCP/IP port 9100; LPR/TCP/IP; Novell remote printer or print server modes; bidirectional or unidirectional Centronics; AppleTalk Data Stream Protocol (ADSP)/EtherTalk; ADSP/LocalTalk; and Novell sequence packet exchange (SPX). These are just a few examples of the constantly increasing number of network protocol/ports that desire "plug and play" connectivity to the network printer.
A printer is a peripheral device that can be shared on a network connected to a print server. Also, a printer can directly connect to the network by including a network interface card or the network interface into the printer which allows the printer to run its own print server software and function as a regular node. In a typical Windows environment, the network printer is a one-way printer. In a one-way printer, the only communication path is from the host computer to the printer. As a result, the data is sent from the host computer to the printer without any ability for the printer to notify the host computer of the job status such as whether the print job has been successfully completed.
The use of a two-way printer has been developed for Macintosh systems (Apple Computer, Cupertino, Calif.). In the AppleTalk protocol used by the Macintosh systems, PAP is the protocol used for communication between the Macintosh host computers and printers. PAP sets up, maintains and terminates the connection between the host computer nodes and the network printer and also transfers the data from the host computers to the printers. PAP allows two-way communication from the network printer to the Macintosh host computer to the extent that the status of the network printer is sent to the Macintosh host computer through PostScript. However, most page description language (PDL) interpreters only allows one job to be processed at one time which prevents asynchronous interaction between multiple clients and the network printer.
Typically, networks utilize shared resource printers. FIG. 1 illustrates the use of a conventional shared resource printer in a network. A plurality of host computers 1.sub.0, 1.sub.1, . . . 1.sub.n and a printer 5 are connected in a network. The printer 5 includes a disk 6 connected internally or externally to the printer 5 for storing the print jobs sent from the host computers 1.sub.0..n before being printed by the printer 5. In shared resource printers, the host computer that first sends a print job to the network printer will have its job printed. Other host computers attempting to have a print job printed by the network printer while another job is being printed will not be able to access the network printer. Therefore, these host computers will repeatedly try to access the network printer during a timing scheme until the network printer becomes available. As a result, the speed of the network will be reduced by the network traffic due to the continuous polling of the host computers to the network printer during the time that the network printer is unavailable. This polling process is undesirable since a host computer will gain access to the printer, with only limited and possibly inexact arbitration after the print job is completed if a number of host computers are attempting to gain access while the printer is busy.
Traditionally, print servers provided access to the network printers and ran the programs necessary to create and operate a print queue for jobs sent to the printers from the host computers. The print queue is a directory that stores into the disk 6 the print jobs waiting to be printed. The print jobs are then printed from the print queue in an FIFO sequence. The print servers require storing the job request and entire job data by spooling this data to the disk 6. Depending on the job size, millions of bytes of data may be spooled to the disk and therefore a large sized disk is necessary.
Even if a large sized disk is used, the disk capacity for storing print jobs may be exceeded when a number of host computers send print jobs to the printer at approximately the same time. When the capacity of the disk is reached, a back up procedure will be implemented where the printer will be polled every two seconds until space in the disk becomes available in a similar manner as in the shared resource printer.
Print servers and a printer may be combined in the same machine on many networks for economical reasons. The main advantage for combining the printer and print servers is that files do not need to be sent from the host computer to the print server machine and then from there to the printer in such a configuration. However, the disadvantage of combining the printer and print servers is that the required control for the print queue and the printing activity takes away CPU time from other network activity. In either case, a disk is required to store the data for the entire print job and since the print job is sent from the host computer, spooled to a disk and then transmitted to the network printer when the printer becomes available, unnecessary network activity results.
Accordingly, it is desired to provide a network printing system which enhances the two-way communication between the host computers and the network printer. Further along these lines, it is desirable to provide a symmetrical protocol for facilitating connections between servers and clients over connection based-stream oriented protocol such as ADSP and TCP.